Re: [PATCH v3 02/10] Change isolate mode from int type to enum type

[Mel Gorman]

On Tue, Jun 07, 2011 at 11:38:15PM +0900, Minchan Kim wrote:
> This patch changes macro define with enum variable.
> Normally, enum is preferred as it's type-safe and making debugging easier
> as symbol can be passed throught to the debugger.
> 
> This patch doesn't change old behavior.
> It is used by next patches.
> 
> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx>
> ---
>  include/linux/memcontrol.h    |    5 ++++-
>  include/linux/swap.h          |   11 +++++++----
>  include/trace/events/vmscan.h |    8 ++++----
>  mm/compaction.c               |    3 ++-
>  mm/memcontrol.c               |    3 ++-
>  mm/migrate.c                  |    4 ++--
>  mm/vmscan.c                   |   37 ++++++++++++++++++++-----------------
>  7 files changed, 41 insertions(+), 30 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 5e9840f..91a1162 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -30,10 +30,13 @@ enum mem_cgroup_page_stat_item {
>  	MEMCG_NR_FILE_MAPPED, /* # of pages charged as file rss */
>  };
>  
> +enum ISOLATE_MODE;
> +

All caps. Really? It's NOT VERY PRETTY AND MAKES MY EYES DEAF WHICH
SHOULD BE IMPOSSIBLE.

What's wrong with

enum isolate_mode {
}

? It's reasonable that the constants themselves are in caps. It's
expected for defines and enum values.

>  extern unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
>  					struct list_head *dst,
>  					unsigned long *scanned, int order,
> -					int mode, struct zone *z,
> +					enum ISOLATE_MODE mode,

I don't mind as much now because I'm already eye-deaf.

> +					struct zone *z,
>  					struct mem_cgroup *mem_cont,
>  					int active, int file);
>  
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index a5c6da5..48d50e6 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -244,9 +244,11 @@ static inline void lru_cache_add_file(struct page *page)
>  }
>  
>  /* LRU Isolation modes. */
> -#define ISOLATE_INACTIVE 0	/* Isolate inactive pages. */
> -#define ISOLATE_ACTIVE 1	/* Isolate active pages. */
> -#define ISOLATE_BOTH 2		/* Isolate both active and inactive pages. */
> +enum ISOLATE_MODE {
> +	ISOLATE_NONE,
> +	ISOLATE_INACTIVE = 1,	/* Isolate inactive pages */
> +	ISOLATE_ACTIVE = 2,	/* Isolate active pages */
> +};

No need to explicitly define like this. i.e. drop the = 1, = 2 etc.

The leader does not explain why ISOLATE_BOTH is replaced and what it
gains us.

>  
>  /* linux/mm/vmscan.c */
>  extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
> @@ -258,7 +260,8 @@ extern unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
>  						gfp_t gfp_mask, bool noswap,
>  						unsigned int swappiness,
>  						struct zone *zone);
> -extern int __isolate_lru_page(struct page *page, int mode, int file);
> +extern int __isolate_lru_page(struct page *page, enum ISOLATE_MODE mode,
> +					int file);
>  extern unsigned long shrink_all_memory(unsigned long nr_pages);
>  extern int vm_swappiness;
>  extern int remove_mapping(struct address_space *mapping, struct page *page);
> diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
> index ea422aa..4f53d43 100644
> --- a/include/trace/events/vmscan.h
> +++ b/include/trace/events/vmscan.h
> @@ -187,7 +187,7 @@ DECLARE_EVENT_CLASS(mm_vmscan_lru_isolate_template,
>  		unsigned long nr_lumpy_taken,
>  		unsigned long nr_lumpy_dirty,
>  		unsigned long nr_lumpy_failed,
> -		int isolate_mode),
> +		enum ISOLATE_MODE isolate_mode),
>  
>  	TP_ARGS(order, nr_requested, nr_scanned, nr_taken, nr_lumpy_taken, nr_lumpy_dirty, nr_lumpy_failed, isolate_mode),
>  
> @@ -199,7 +199,7 @@ DECLARE_EVENT_CLASS(mm_vmscan_lru_isolate_template,
>  		__field(unsigned long, nr_lumpy_taken)
>  		__field(unsigned long, nr_lumpy_dirty)
>  		__field(unsigned long, nr_lumpy_failed)
> -		__field(int, isolate_mode)
> +		__field(enum ISOLATE_MODE, isolate_mode)
>  	),
>  
>  	TP_fast_assign(
> @@ -233,7 +233,7 @@ DEFINE_EVENT(mm_vmscan_lru_isolate_template, mm_vmscan_lru_isolate,
>  		unsigned long nr_lumpy_taken,
>  		unsigned long nr_lumpy_dirty,
>  		unsigned long nr_lumpy_failed,
> -		int isolate_mode),
> +		enum ISOLATE_MODE isolate_mode),
>  
>  	TP_ARGS(order, nr_requested, nr_scanned, nr_taken, nr_lumpy_taken, nr_lumpy_dirty, nr_lumpy_failed, isolate_mode)
>  
> @@ -248,7 +248,7 @@ DEFINE_EVENT(mm_vmscan_lru_isolate_template, mm_vmscan_memcg_isolate,
>  		unsigned long nr_lumpy_taken,
>  		unsigned long nr_lumpy_dirty,
>  		unsigned long nr_lumpy_failed,
> -		int isolate_mode),
> +		enum ISOLATE_MODE isolate_mode),
>  

And the meaning of isolate_mode has changed. This affects users of the
tracepoint. Documentation/trace/postprocess/trace-vmscan-postprocess.pl
will consider ISOLATE_NONE to be scanning for example.

>  	TP_ARGS(order, nr_requested, nr_scanned, nr_taken, nr_lumpy_taken, nr_lumpy_dirty, nr_lumpy_failed, isolate_mode)
>  
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 61eab88..f0d75e9 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -327,7 +327,8 @@ static unsigned long isolate_migratepages(struct zone *zone,
>  		}
>  
>  		/* Try isolate the page */
> -		if (__isolate_lru_page(page, ISOLATE_BOTH, 0) != 0)
> +		if (__isolate_lru_page(page,
> +				ISOLATE_ACTIVE|ISOLATE_INACTIVE, 0) != 0)

Ahh, so you assign the enum to user it as a flag. That's very
unexpected to me. Why did you not do something like gfp_t which is a
bitwise type?

Because mode is a bitmask, it's also impossible to check if
ISOLATE_NONE is set. As ISOLATE_NONE is not used in this patch,
it's hard to know at this point what it's for.

>  			continue;
>  
>  		VM_BUG_ON(PageTransCompound(page));
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 010f916..f4c0b71 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1106,7 +1106,8 @@ mem_cgroup_get_reclaim_stat_from_page(struct page *page)
>  unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
>  					struct list_head *dst,
>  					unsigned long *scanned, int order,
> -					int mode, struct zone *z,
> +					enum ISOLATE_MODE mode,
> +					struct zone *z,
>  					struct mem_cgroup *mem_cont,
>  					int active, int file)
>  {
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 819d233..e797b5c 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1363,10 +1363,10 @@ int migrate_vmas(struct mm_struct *mm, const nodemask_t *to,
>  
>  	for (vma = mm->mmap; vma && !err; vma = vma->vm_next) {
>   		if (vma->vm_ops && vma->vm_ops->migrate) {
> - 			err = vma->vm_ops->migrate(vma, to, from, flags);
> + 			err = vma->vm_ops->migrate(vma, to, from, flags);   
>   			if (err)
>   				break;
> - 		}
> + 		}     

Only modification here is adding whitespace damage.

>   	}
>   	return err;
>  }
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a658dde..4cbe114 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -957,23 +957,27 @@ keep_lumpy:
>   *
>   * returns 0 on success, -ve errno on failure.
>   */
> -int __isolate_lru_page(struct page *page, int mode, int file)
> +int __isolate_lru_page(struct page *page, enum ISOLATE_MODE mode, int file)
>  {
> +	bool all_lru_mode;
>  	int ret = -EINVAL;
>  
>  	/* Only take pages on the LRU. */
>  	if (!PageLRU(page))
>  		return ret;
>  
> +	all_lru_mode = (mode & (ISOLATE_ACTIVE|ISOLATE_INACTIVE)) == 
> +		(ISOLATE_ACTIVE|ISOLATE_INACTIVE);
> +

both_lru would be a better name because all LRU implies that UNEVICTABLE
is involved which is not the case.

>  	/*
>  	 * When checking the active state, we need to be sure we are
>  	 * dealing with comparible boolean values.  Take the logical not
>  	 * of each.
>  	 */
> -	if (mode != ISOLATE_BOTH && (!PageActive(page) != !mode))
> +	if (!all_lru_mode && !PageActive(page) != !(mode & ISOLATE_ACTIVE))
>  		return ret;
>  
> -	if (mode != ISOLATE_BOTH && page_is_file_cache(page) != file)
> +	if (!all_lru_mode && !!page_is_file_cache(page) != file)
>  		return ret;
>  
>  	/*
> @@ -1021,7 +1025,8 @@ int __isolate_lru_page(struct page *page, int mode, int file)
>   */
>  static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>  		struct list_head *src, struct list_head *dst,
> -		unsigned long *scanned, int order, int mode, int file)
> +		unsigned long *scanned, int order, enum ISOLATE_MODE mode,
> +		int file)
>  {
>  	unsigned long nr_taken = 0;
>  	unsigned long nr_lumpy_taken = 0;
> @@ -1134,8 +1139,8 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>  static unsigned long isolate_pages_global(unsigned long nr,
>  					struct list_head *dst,
>  					unsigned long *scanned, int order,
> -					int mode, struct zone *z,
> -					int active, int file)
> +					enum ISOLATE_MODE mode,
> +					struct zone *z,	int active, int file)
>  {
>  	int lru = LRU_BASE;
>  	if (active)
> @@ -1382,6 +1387,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
>  	unsigned long nr_taken;
>  	unsigned long nr_anon;
>  	unsigned long nr_file;
> +	enum ISOLATE_MODE reclaim_mode = ISOLATE_INACTIVE;
>  
>  	while (unlikely(too_many_isolated(zone, file, sc))) {
>  		congestion_wait(BLK_RW_ASYNC, HZ/10);
> @@ -1392,15 +1398,15 @@ shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
>  	}
>  
>  	set_reclaim_mode(priority, sc, false);
> +	if (sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM)
> +		reclaim_mode |= ISOLATE_ACTIVE;
> +
>  	lru_add_drain();
>  	spin_lock_irq(&zone->lru_lock);
>  
>  	if (scanning_global_lru(sc)) {
> -		nr_taken = isolate_pages_global(nr_to_scan,
> -			&page_list, &nr_scanned, sc->order,
> -			sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM ?
> -					ISOLATE_BOTH : ISOLATE_INACTIVE,
> -			zone, 0, file);
> +		nr_taken = isolate_pages_global(nr_to_scan, &page_list,
> +			&nr_scanned, sc->order, reclaim_mode, zone, 0, file);
>  		zone->pages_scanned += nr_scanned;
>  		if (current_is_kswapd())
>  			__count_zone_vm_events(PGSCAN_KSWAPD, zone,

While this looks ok, I do not see why it's better.

> @@ -1409,12 +1415,9 @@ shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
>  			__count_zone_vm_events(PGSCAN_DIRECT, zone,
>  					       nr_scanned);
>  	} else {
> -		nr_taken = mem_cgroup_isolate_pages(nr_to_scan,
> -			&page_list, &nr_scanned, sc->order,
> -			sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM ?
> -					ISOLATE_BOTH : ISOLATE_INACTIVE,
> -			zone, sc->mem_cgroup,
> -			0, file);
> +		nr_taken = mem_cgroup_isolate_pages(nr_to_scan, &page_list,
> +			&nr_scanned, sc->order, reclaim_mode, zone,
> +			sc->mem_cgroup, 0, file);
>  		/*
>  		 * mem_cgroup_isolate_pages() keeps track of
>  		 * scanned pages on its own.

Overall, I'm failing to see how this patch helps but maybe it's because
I haven't read the rest of the series. My main gripe is that meaning
of isolate_mode in the tracepoint has changed without any clear gain.

-- 
Mel Gorman
SUSE Labs
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